1. Field of the Invention
The present invention relates to an adjusting device for adjustably varying a tilt angle of a tilting axis of an axial piston pump/motor of a tilting axis type.
2. Description of the Prior Art
An adjusting device for an axial piston pump/motor of a tilting axis type in which a tilt angle of a valve plate is varied by rocking the valve plate along arcuate guide grooves provided in an end cover, has been heretofore known.
One example of such adjusting devices for an axial piston pump/motor of a tilting axis type in the prior art, is illustrated in FIG. 1. In this figure, reference numeral 1 designates a casing, numeral 2 designates a drive shaft supported by the casing 1, numeral 3 designates a cylinder block, numeral 4 designates a valve plate held in slide contact with a bottom surface of the cylinder block 3, numeral 5 designates a center pin fitted in an axial center bore of the cylinder block 3 and having its tip end pivotably supported by an axial center portion of the drive shaft 2, numeral 6 designates a plurality of cylinder bores disposed in the cylinder block 3 as arrayed in a circumferential direction, numeral 7 designates pistons fitted in the respective cylinder bores 6, and these pistons 7 are pivotably mounted to a tip end of the drive shaft 2 via a retainer 8. Reference numeral 9 designates a spring for biasing the cylinder block 3 towards the valve plate 4.
Reference numeral 11 designates an adjusting device, as a whole, for varying displacement of a pump/motor by rocking the above-mentioned valve plate 4 in one direction, and numeral 12 designates an end cover provided with guide grooves 13 for supporting and guiding the valve plate 4 so as to allow rocking thereof about the pivotal fulcrum of the center pin 5. In this end cover 12 is provided a cylinder 14 directed in the direction of rocking of the valve plate 4, and a single piston 15 is fitted in this cylinder 14. Reference numerals 16a and 16b, respectively, designate lids for closing the opposite ends of the cylinder 14. In the central portion along the longitudinal direction of the cylinder 14 is provided an aperture 14a opening in the bottom surface of the above-described guide grooves 13 as extending over the rocking range of the valve plate 4. A trunnion pin 17 is studded in the portion of this piston 15 opposed to the aperture 14a, and a tip end portion of this trunnion pin 17 is rockably engaged with an axial center portion of the valve plate 4.
In the sector-shaped variable displacement piston pump/motor as described above, the valve plate 4 is made to rock along the guide prooves 13 provided in the end cover 12 via the trunnion pin 17 by reciprocating the piston 15, thereby a tilt angle of the cylinder block 3 with respect to the drive shaft 2 is varied, and hence, the displacement of the piston pump/motor can be varied.
In the above-described adjusting device 11 for an axial piston pump/motor of a tilting axis type in the prior art, since the stroke of the piston 15 and the rocking range (distance) of the valve plate 4 have the relation of 1:1, while the rocking radius of the valve plate 4 can be chosen to be large and hence the manipulation force can be made small, on the other hand the stroke of the piston 15 becomes long, and hence there was a problem that the adjusting device would become large-sized in the direction of stroke of the piston 15.